1. Field of Invention
The present invention relates to clutches for controlling the motion of snow throwers and other walk-behind lawn and garden implements, particularly for steering these implements.
2. Description of the Related Art
Lawn and garden implements, for example, mowers, tillers and snow throwers, often comprise a transaxle through which power from an engine is transmitted to ground-engaging wheels attached to axles extending from the transaxle for propelling the implement. These implements are often difficult to steer, owing to their weight, size or the particular way in which the geartrain of the transaxle is designed. As to their geartrain design, many transaxles are provided with a solid axle which transmits an equal amount of torque to each of the pair of ground-engaging wheels, and during a turn, the wheel at the inside of the turn rotates at the same speed as the wheel at the outside of the turn; the wheel at the inside of the turn must be skidded on the ground to some degree, a considerable degree for sharp turns, in order to negotiate the turn. Controlling the implement can thus be a problem for some operators having insufficient strength or weight to force the implement through the turn as desired.
Previous attempts to address this problem include providing the transaxle with a differential, which allows the two ground-engaging wheels to rotate at different speeds, as is well known in the art. Through use of a differential, the wheel at the inside of the turn is not skidded on the ground during the turn; rather it slows down, while the wheel at the outside of the turn correspondingly speeds up. Differential arrangements, while improving the amount of control during cornering, add considerable cost to the transaxle. Moreover, even if the implement is provided with a differential-equipped transaxle, a not insubstantial amount of force is still required to initiate the turn and hold the implement therethrough. Thus, transaxles having differential arrangements do not provide satisfactorily controllable implements for all operators.
Another possible approach is the use of clutches to control the implement by powering or disengaging power from the ground engaging wheels. Some clutches which provide some control over the powering of an implement or other device include means for selective disengagement of the input and output members (see, e.g., U.S. Pat. Nos. Re. 25,229, 2,951,568, and 3,429,408); other clutches require that the spring expand to produce engagement between the input and output members (see, e.g., U.S. Pat. Nos. 3,040,855 and 5,029,689); still other clutches use additional elements such as solenoids to cause the contraction of the spring (see, e.g., U.S. Pat. Nos. 3,726,372 and 4,191,283). Currently available clutch mechanisms may also use hand grip-mounted triggers to engage and disengage the clutch. Such systems do provide means for simple engagement and disengagement of the clutches, but do not provide the selective steering capabilities needed for a person of smaller stature to easily control the turning of the implement.
Another alternative has been steering mechanisms which use overrunning clutches at each wheel. These mechanisms disengage power transfer to the inside wheel when the implement is turned. A problem with these systems is that they could prove to be too sensitive when the implement is used on rough ground, such as hilly areas where the implement experiences a turning effect even when the operator travels in a straight line. Another shortcoming of such steering systems is that the overrunning clutches may allow the implement to freewheel on downhill grades as the weight of the implement causes the wheels to turn at a rate faster than the axle, possibly resulting in at least a temporary increase in implement ground speed.
An implement which is easily controlled and steered, even by an operator of small stature or insufficient weight to otherwise easily turn the implement, without great additional expense or complexity, and overcomes the above-described shortcomings of the prior art, would be highly desirable.
The above-described shortcomings of previous implements are effectively addressed by the present invention, which provides a means for improving implement control and steering as well as providing such control and steering easily and inexpensively.
The present invention provides a reversible implement including an engine, an axle driven by the engine, a pair of ground engaging wheels with one of the wheels being located at each end of the axle, a pair of input hubs with each input hub being rotatably fixed to the axle, a pair of wheel hubs with one of the wheel hubs being located at each end of the axle and attached to one of the ground engaging wheels, and a wrap spring surrounding a portion of each input hub and each wheel hub. Each wrap spring has a relaxed state, wherein the wrap spring is in one of a first position in which the wrap spring is disengaged from the wheel hub, and the input and wheel hubs are not rotatively coupled together, and a second position in which the wrap spring is engaged with the wheel hub, and the input and wheel hubs are rotatively coupled together, and a contracted state, wherein the wrap spring is in the other of the positions.
The present invention further provides an implement including an engine, an axle driven by the engine and having an input hub attached to each end thereof, a pair of ground engaging wheels with one of the wheels being located at each end of the axle and each wheel having a wheel hub attached thereto, a wrap spring disposed around a portion of each input hub and each wheel hub and selectively engaging each wheel hub, and a rotatable control collar surrounding each wrap spring. The control collar has a non-rotating state wherein the wrap spring is disengaged from the wheel hub and a rotating state wherein the wrap spring is in engagement with the wheel hub.
The present invention also provides a reversible implement including an engine, an axle driven by the engine, a pair of ground engaging wheels with one of the wheels being located at each end of the axle, a pair of input hubs with each input hub being rotatably fixed to the axle, a pair of wheel hubs with one of the wheel hubs being located at each end of the axle and attached to one of the ground engaging wheels, a wrap spring surrounding a portion of each input hub and each wheel hub, and a rotatable control collar surrounding each wrap spring. Each wrap spring has a relaxed state, wherein the wrap spring is in one of a first position in which the wrap spring is disengaged from the wheel hub, and the input and wheel hubs are not rotatively coupled together, and a second position in which the wrap spring is engaged with the wheel hub, and the input and wheel hubs are rotatively coupled together, and a contracted state, wherein the wrap spring is in the other of the positions. The rotatable control collar is movable between a non-rotating state wherein the wrap spring is in its relaxed state and a rotating state wherein the wrap spring is urged into its contracted state.